Quick Question about O2 bottle

[JS1scuba]

...unless you now have more (or bigger) bottles than you can easily handle, which in itself is a hazard...everything in balance.

Balance is assumed. Proper planning with proper equipment.
in the 250 / 25 min profile -- sure a full 40 of oxgyen is more than enough. It calls for 20 cuft -- even at 30 min you only need 30 cuft --- using a ratio deco or bubble model --- move off to a neo-haldanean model either table or computer based and the whole shape changes and the gas requirements - now that 25 or 30 min BT will suck the 40 dry if you end up with any activity. It's all in the shape of the deco - both are right -- the neo haldanean models seem to work better in caves where the decompression shape is based on the physical environment -- whereas RD / bubble work better for open water.

Cheers
JDS

[Dive-aholic]

25 @ 250 is about 75 mins deco. With a 120 bottle, that gives about 30 mins on an O2 bottle.
Estimating at 60psi/min on the bottle, thats 1800 psi (if you count BG breaks in the O2 time)

Thats easily enough (1200 psi since I get 3000 fills) to cover a lost bottle.

Yes, if I was only getting cascaded 2000-2200 psi fills then obviously a 40 isn't enough.

It depends on how you plan your dive. I'm more conservative than that. Here's a dive to 250' for 15 minutes (10 minutes to get to 250) using V-Planner. Note the required O2 and 50% using an RMV of .5. A 40 of each isn't going to be enough. This is a cave. In OW you would get to 250 much faster.

Dec to 130ft (2) on Trimix 13.0/50.0, 50ft/min descent.
Level 130ft 2:24 (5) on Trimix 13.0/50.0, 0.63 ppO2, 43ft EAD
Dec to 200ft (6) on Trimix 13.0/50.0, 50ft/min descent.
Level 200ft 3:36 (10) on Trimix 13.0/50.0, 0.90 ppO2, 76ft EAD
Dec to 250ft (10) on Trimix 13.0/50.0, 60ft/min descent.
Level 250ft 14:10 (25) on Trimix 13.0/50.0, 1.09 ppO2, 99ft EAD
Asc to 190ft (27) on Trimix 13.0/50.0, -30ft/min ascent.
Stop at 180ft 1:00 (28) on Trimix 13.0/50.0, 0.82 ppO2, 66ft EAD
Stop at 170ft 1:00 (29) on Trimix 13.0/50.0, 0.78 ppO2, 62ft EAD
Stop at 160ft 1:00 (30) on Trimix 13.0/50.0, 0.74 ppO2, 57ft EAD
Stop at 150ft 2:00 (32) on Trimix 13.0/50.0, 0.70 ppO2, 52ft EAD
Stop at 140ft 2:00 (34) on Trimix 13.0/50.0, 0.67 ppO2, 48ft EAD
Stop at 130ft 2:00 (36) on Trimix 13.0/50.0, 0.63 ppO2, 43ft EAD
Stop at 120ft 3:00 (39) on Trimix 13.0/50.0, 0.59 ppO2, 38ft EAD
Stop at 110ft 3:00 (42) on Trimix 13.0/50.0, 0.55 ppO2, 33ft EAD
Stop at 100ft 4:00 (46) on Trimix 13.0/50.0, 0.51 ppO2, 29ft EAD
Stop at 90ft 5:00 (51) on Trimix 13.0/50.0, 0.47 ppO2, 24ft EAD
Stop at 80ft 7:00 (58) on Trimix 13.0/50.0, 0.44 ppO2, 19ft EAD
Stop at 70ft 3:00 (61) on Nitrox 50.0, 1.53 ppO2, 32ft EAD
Stop at 60ft 4:00 (65) on Nitrox 50.0, 1.38 ppO2, 26ft EAD
Stop at 50ft 6:00 (71) on Nitrox 50.0, 1.24 ppO2, 19ft EAD
Stop at 40ft 7:00 (78) on Nitrox 50.0, 1.09 ppO2, 13ft EAD
Stop at 30ft 12:00 (90) on Nitrox 50.0, 0.94 ppO2, 7ft EAD
Stop at 20ft 8:00 (98) on Oxygen, 1.59 ppO2, 0ft EAD
Stop at 20ft 5:00 (103) on Trimix 13.0/50.0, 0.21 ppO2, 0ft EAD
Stop at 20ft 20:00 (123) on Oxygen, 1.59 ppO2, 0ft EAD
Stop at 20ft 5:00 (128) on Trimix 13.0/50.0, 0.21 ppO2, 0ft EAD
Stop at 20ft 10:00 (138) on Oxygen, 1.59 ppO2, 0ft EAD
Asc to sfc. (138) on Oxygen, -30ft/min ascent.

Off gassing starts at 204.7 ft

OTU's this dive: 142
CNS Total: 82.0%

171.2 cu ft Trimix 13.0/50.0
36.4 cu ft Nitrox 50.0
30.4 cu ft Oxygen
237.9 cu ft TOTAL



Here's the same dive to 270' for 25 minutes in OW with a direct descent. Note that you still do not have enough deco gas if the sh!t hits the fan.

Dec to 200ft (4) on Trimix 12.0/50.0, 50ft/min descent.
Dec to 250ft (4) on Trimix 12.0/50.0, 60ft/min descent.
Level 250ft 20:10 (25) on Trimix 12.0/50.0, 1.00 ppO2, 103ft EAD
Asc to 190ft (27) on Trimix 12.0/50.0, -30ft/min ascent.
Stop at 180ft 1:00 (28) on Trimix 12.0/50.0, 0.76 ppO2, 69ft EAD
Stop at 170ft 1:00 (29) on Trimix 12.0/50.0, 0.72 ppO2, 64ft EAD
Stop at 160ft 1:00 (30) on Trimix 12.0/50.0, 0.69 ppO2, 59ft EAD
Stop at 150ft 2:00 (32) on Trimix 12.0/50.0, 0.65 ppO2, 55ft EAD
Stop at 140ft 2:00 (34) on Trimix 12.0/50.0, 0.62 ppO2, 50ft EAD
Stop at 130ft 2:00 (36) on Trimix 12.0/50.0, 0.58 ppO2, 45ft EAD
Stop at 120ft 3:00 (39) on Trimix 12.0/50.0, 0.54 ppO2, 40ft EAD
Stop at 110ft 4:00 (43) on Trimix 12.0/50.0, 0.51 ppO2, 35ft EAD
Stop at 100ft 4:00 (47) on Trimix 12.0/50.0, 0.47 ppO2, 31ft EAD
Stop at 90ft 6:00 (53) on Trimix 12.0/50.0, 0.44 ppO2, 26ft EAD
Stop at 80ft 7:00 (60) on Trimix 12.0/50.0, 0.40 ppO2, 21ft EAD
Stop at 70ft 4:00 (64) on Nitrox 50.0, 1.53 ppO2, 32ft EAD
Stop at 60ft 4:00 (68) on Nitrox 50.0, 1.38 ppO2, 26ft EAD
Stop at 50ft 6:00 (74) on Nitrox 50.0, 1.24 ppO2, 19ft EAD
Stop at 40ft 8:00 (82) on Nitrox 50.0, 1.09 ppO2, 13ft EAD
Stop at 30ft 12:00 (94) on Nitrox 50.0, 0.94 ppO2, 7ft EAD
Stop at 20ft 8:00 (102) on Oxygen, 1.59 ppO2, 0ft EAD
Stop at 20ft 5:00 (107) on Trimix 12.0/50.0, 0.19 ppO2, 0ft EAD
Stop at 20ft 20:00 (127) on Oxygen, 1.59 ppO2, 0ft EAD
Stop at 20ft 5:00 (132) on Trimix 12.0/50.0, 0.19 ppO2, 0ft EAD
Stop at 20ft 13:00 (145) on Oxygen, 1.59 ppO2, 0ft EAD
Asc to sfc. (145) on Oxygen, -30ft/min ascent.

Off gassing starts at 210.4 ft

OTU's this dive: 149
CNS Total: 86.8%

182.0 cu ft Trimix 12.0/50.0
39.0 cu ft Nitrox 50.0
32.8 cu ft Oxygen
253.8 cu ft TOTAL


Oh, and I'm boosting my O2 to 3200psi. No cascading in my calculations.



Joel, one of my favorite sayings it no one ever died from having too much gas!

[JS1scuba]

who commercially fills pure oxygen without a booster ? that's silly

[Rainer]

Rob, if you add deeper deco gases (so you don't have to travel 200' if there's a problem with backgas on the bottom...) you'll also shorten up that required O2 deco. As Nick noted in his post, he's at least adding a 120' bottle (35/25).

[Mo2vation]

who fills pure oxygen without a booster ? that's silly

uh, most of us ghetto home blenders, buddy.




-K

[JS1scuba]

uh, most of us ghetto home blenders, buddy.




-K

commercially --- though ghetto fillers need to get a ghetto booster ..........

[AzTek Diver]

commercially --- though ghetto fillers need to get a ghetto booster ..........

While I have a Haskel, by getting my O2 bottles from my supplier at 3600 it gets almost no use on O2, Helium on the other hand works it hard.

[Mo2vation]

While I have a Haskel, by getting my O2 bottles from my supplier at 3600 it gets almost no use on O2, Helium on the other hand works it hard.

3600.

Really?

Dude, you were my hero. Now you're my idol.




-Ken

[Mo2vation]

commercially --- though ghetto fillers need to get a ghetto booster ..........

I SO need a ghetto booster.

I need to bust out The Vance, hit up my local pick-a-part for some crusty floor jack and build me a proper ghetto booster.

Somewhere in this process, i should probably, you know, in the name of all that is neighborly, distribute fliers to the surrounding dwellings.

-K

[Dive-aholic]

Rob, if you add deeper deco gases (so you don't have to travel 200' if there's a problem with backgas on the bottom...) you'll also shorten up that required O2 deco. As Nick noted in his post, he's at least adding a 120' bottle (35/25).

True, but that adds a 3rd bottle and only ends up shortening my deco by about 15 minutes.

[Rainer]

Yup, it adds one bottle (an AL40) but significantly cuts down on rock bottom / min gas, so you could probably use smaller doubles (or even eliminate a bottom stage), and you could safely now use an AL40 for O2 instead of an AL80. Seems a net win. Also a fair amount more flexibility for lost back/deco gas schedules.

True, but that adds a 3rd bottle and only ends up shortening my deco by about 15 minutes.

[Kc1Scuba]

I SO need a ghetto booster.

Somewhere in this process, i should probably, you know, in the name of all that is neighborly, distribute fliers to the surrounding dwellings.

-K

I can only imagine how humorous and creative these said fliers could actually be. lol

[Nick Ambrose]

Yup, it adds one bottle (an AL40) but significantly cuts down on rock bottom / min gas, so you could probably use smaller doubles (or even eliminate a bottom stage), and you could safely now use an AL40 for O2 instead of an AL80. Seems a net win. Also a fair amount more flexibility for lost back/deco gas schedules.

Indeed, min gas without the 120 bottle starts to get pretty big at 270.

[Nick Ambrose]

It depends on how you plan your dive. I'm more conservative than that. Here's a dive to 250' for 15 minutes (10 minutes to get to 250) using V-Planner. Note the required O2 and 50% using an RMV of .5. A 40 of each isn't going to be enough. This is a cave. In OW you would get to 250 much faster.

...{lots of numbers snipped}

Joel, one of my favorite sayings it no one ever died from having too much gas!

Not sure why a 25 min dive needs more deco time in a cave than in open water honestly.

For 25 @ 275 I only need 28cft of O2 (35 mins) assuming i dont do O2 breaks (less with the breaks)

While adding a deco bottle in a cave is relatively simple, for me upsizing or adding a bottle in open water is a much more considered option because they quickly start to significantly add to the task loading when managing them.

I dont have enough cave deco experience to comment too much on the practical application (and with respect I would venture neither does Joel

But yes, depending on the cave I can imagine one would try to take advantage of that if possible during deco.

[Seainggreen]

Yup, it adds one bottle (an AL40) but significantly cuts down on rock bottom / min gas, so you could probably use smaller doubles (or even eliminate a bottom stage), and you could safely now use an AL40 for O2 instead of an AL80. Seems a net win. Also a fair amount more flexibility for lost back/deco gas schedules.

Cutting 15 mins of deco when water temps are 50F and below is definitely worthwhile. Beyond that, I find diving with multiple AL40s easier than multiple Al80s. The size of multiple 80s is a factor for me (I am 5'6" on a good day and arm length around bottles can be a challenge), plus dealing with them on rotations is less preferable than handling 40s. That's just me. On that note, if the dive allowed for it I'd go with bigger backgas volume and lose the stage. But I haven't found many dives beyond 200 where that's a safe option while still giving decent BT and reserve gas.

I agree with Nick that you really have to look at adding/subtracting bottles more carefully in OW than cave because you're carrying them all for the full dive, and then managing and moving them on you the whole time. I'm not sure if this makes sense, but in cave a lot of the mental work (remembering to put a specific bottle in a specific spot) happens on the setup on the way in and then on the way home you're stowing the used bottle and confirming/picking up the next one you need. Plus you're not carrying everything with you the whole time, which is nice. In OW a lot of the mental work happens on the way home as you have to rotate around used and new bottles in an organized fashion and keep track of which went where all the way home and you're lugging them all with you all the time. So I think very carefully about just what is needed and plan accordingly.